China burns more coal than the rest of the world combined. It also manufactures more than 80% of the world’s solar panels and may have already peaked its emissions years ahead of schedule. It accounts for roughly a third of global CO₂ emissions—more than the United States, the European Union, and Japan combined. Yet under the United Nations Framework Convention on Climate Change (UNFCCC), the treaty that has governed international climate negotiations since 1992, it sits in the same legal category as Burundi, Somalia, and the Central African Republic: “developing.” That classification is not simply wrong. China’s per capita emissions remain well below those of the United States, and roughly a quarter of its population (some 350 million people) still lives in poverty by the World Bank’s measure. But the label is not adequate either. The UNFCCC’s binary framework (developed countries in one column, developing in the other) was never built to accommodate a country that belongs, however imperfectly, in both—and its governing principle, common but differentiated responsibilities (CBDR), offers no middle ground. Cass Sunstein’s …